A review of emerging technology using membranes to separate acid gases such as CO.sub.2, H.sub.2 S and SO.sub.2 from gas streams is disclosed by S. Kulkarni, et al. in an article entitled, "Membrane Separation Processes for Acid Gases," AIChE Symposium Series (1983). Both currently available and potential polymer membranes for the separation of CO.sub.2 from natural gas are disclosed. The permeation characteristics of various types of membranes, such as asymmetric cellulose esters, multi-component polysulfone/silicon rubber, ultrathin polyetherimide, and ultrathin silicone rubber/polycarbonate, were calculated for CO.sub.2 /CH.sub.4 gas mixtures.
U.S. Pat. No. 4,486,202 discloses gas separation membranes exhibiting improved gas separation selectivity. A preformed, asymmetrical gas separation membrane having selective permeation of at least one gas in a gaseous mixture over that of one or more remaining gases in the gaseous mixture, is contacted on one or both sides with a Lewis acid. Contacting the asymmetrical membrane with a Lewis acid results in improved separation factors for the permeating gases. The patent also discloses a method for producing improved, asymmetrical membranes in flat film or hollow fiber form having improved gas separation properties by treatment with a volatile Lewis acid.
U.S. Pat. No. 4,472,175 discloses gas separation membranes exhibiting improved gas separation selectivity. In this patent, a preformed, asymmetrical gas separation membrane, having selective permeation for at least one gas in a gaseous mixture over that of one or more remaining gases in a gaseous mixture, is contacted on one or both sides with a Bronsted-Lowry acid. Contacting the asymmetrical membrane with a Bronsted-Lowry acid results in improved separation factors for the permeating gases. Additionally, this patent discloses a method for producing improved, asymmetric membranes in flat film or hollow fiber form having improved gas separation properties by treatment with a Bronsted-Lowry acid.
U.K. patent application No. 2135319A discloses a membrane having improved permeability for a variety of gases. The membrane is formed from a polymer having repeating units of the formula: ##STR3## wherein R is an alkyl radical having 1-12 carbon atoms. The polymer is dissolved in one or more solvents, such as aliphatic hydrocarbons, to form a polymer solution which is cast to form a film. The membranes may be produced in any form, such as plain film, tubular and hollow fibrous forms and, if necessary, may be supported on one or more backing layers to form composites.
U.S. Pat. No. 4,020,223 discloses a method of modifying the surface of synthetic resins selected from the group consisting of polyolefins and polyacrylonitriles by treatment with a fluorine-containing gas. The fluorinated resin fibers exhibit good soil release and good water adsorption or moisture transport properties.